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CHARACTERISTICS A tropical wave is normally preceded by an area of sinking, intensely dry air, oriented as a northeast wind. With the passage of the trough line, the wind veers to the southeast, the humidity abruptly rises, and the atmosphere destabilizes, producing widespread showers and thunderstorms, occasionally severe. As the wave moves off westward, the showers gradually diminish. A notable exception to the general characteristic of widespread precipitation behind a tropical wave occurs in the Atlantic. Periodically, a surge of intensely dry air known as the Saharan Air Layer (SAL) is entrained behind a tropical wave, resulting in cloudless or nearly cloudless skies as convection is capped by the dry layer inversion. Additionally, any dust which may be present within the SAL reflects solar radiation, slightly cooling the atmosphere below it. ATLANTIC Tropical waves in the Atlantic basin develop from disturbances which drift off the continent of Africa onto the Atlantic Ocean . These are generated or enhanced by the African Easterly Jet . The clockwise circulation of the large transoceanic High-pressure Cell or Anticyclone centered near the Azores islands impels easterly waves away from the coastal areas of Africa towards North America . Approximately 60% of Atlantic Tropical Cyclones originate from tropical waves, while approximately 85% of intense Atlantic hurricanes ( Category 3 and greater) develop from tropical waves.1 Tropical cyclones can sometimes degenerate back into a tropical wave. This normally occurs if upper-level Wind Shear is too strong. The storm can redevelop if the upper level shear abates. If a tropical wave is moving quickly, it can have strong winds of over tropical storm force, but is not considered a tropical storm unless it has a closed circulation. An example of this was Hurricane Claudette in 2003 , where the original wave had winds of before developing a circulation. EAST PACIFIC It has been suggested that eastern Pacific Ocean tropical cyclones are formed out of tropical waves that originate in North Africa as well. During the summer months, tropical waves can extend northward as far as the desert southwest of the United States, producing spells of intensified shower activity embedded within the prevailing Monsoon regime. SEE ALSO REFERENCES EXTERNAL LINKS
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